Wireless communication systems have become ubiquitous in society. Business and consumers use a wide variety of fixed and mobile wireless terminals, including cell phones, pagers, Personal Communication Services (PCS) systems, and fixed wireless access devices (e.g., vending machine with cell phone capability). Wireless service providers continually try to create new markets for wireless devices and expand existing markets by making wireless devices and services cheaper and more reliable. The prices of wireless devices have decreased to the point where nearly everyone can afford them. To continue to attract new customers, wireless service providers are implementing new services, especially digital data services that, for example, enable a user (or subscriber) to browse the Internet and to send and receive e-mail.
Mobile stations (e.g., cell phones, PCS handsets, portable computers, telemetry devices, and the like) frequently operate from an external power source connected to the mobile station. When the external power source is not connected, an internal battery provides a limited period of operation. Mobile stations that operate from batteries for longer periods of time offer increased value to users and competitive advantages for service providers and equipment vendors.
The duration of mobile station battery operation has often been extended using techniques that lower power consumption when the mobile station is in an idle state and not transferring voice or data traffic. A mobile station may enable one or more power saving configurations when it is in the idle state. For instance, the mobile station may disable its transmitter during the idle state, decreasing the amount of power required for idle state operation. A mobile station may further reduce its idle state power requirements by enabling a slotted mode of operation with a base station.
A mobile station enters the idle state when the mobile station is turned on, is synchronized with the system, and has no calls in progress. During the idle state, a mobile station actively listens to a paging channel for information. This information includes overhead messages, such as system parameter messages, as well as messages directly addressed to the mobile station from a base station. A mobile station in the idle state may operate from a battery or from an external power source.
During the idle state, the mobile station may communicate with a base station in a non-slotted or a slotted mode. A typical paging channel slot is an 80-millisecond time slot within a paging slot cycle. The paging slot cycle ranges from 16 time slots (1.28 seconds) to 2048 time slots (163.84 seconds). In the non-slotted mode, the mobile station monitors all paging channel slots for messages from the base station. In the slotted mode, the mobile station only monitors a selected subset of the paging channel slots for messages from the base station. During time periods when the mobile station is not monitoring the selected subset of paging channel slots, power is turned off in the mobile station RF receiver in order to save additional power. A mobile station extends the battery supply operating life by entering a slotted mode of operation with the base station because the mobile station receiver consumes power only during selected slot cycles rather than across the entire paging cycle.
In earlier wireless networks, such as Release B of cdma2000 (i.e., IS-2000-B), the mobile station could select a full slot cycle index, r, between 0 and 7 (i.e., 000-111). The slot cycle index, r, gives the period, P, of the slotted mode of operation according to the equation:P=(2)r×1.28 seconds.  [Eqn. 1]Thus, for example, if the full slot cycle index, r, is 0, the period of the slotted mode is 1.28 seconds. If the full slot cycle index, r, is 7, the period of the slotted mode is 163.84 seconds.
However, the latest generation of wireless terminals, particularly cell phones and other mobile stations, incorporate new features and applications that require very fast messaging. Many of these new features cannot operate with full cycle slotted mode periods of 1.28 seconds or greater. For example, many cell phones and other wireless mobile stations (e.g., Palm Pilot) support interactive gaming applications that enable the operator of one mobile station to play against the operator of another mobile station. However, a gaming application that requires fast, real-time interactions cannot properly operate in a slotted mode that has a minimum period of 1.28 seconds.
Another new application that is adversely affected by full cycle slotted mode operation is Push-to-Talk service, such as the Direct ConnectSM service available from Nextel. A Push-to-Talk service allows two mobile stations to operate as walkie-talkies. A call connection is set up between a first mobile station and a second mobile station. After the call connection is established, the operators may let both mobile stations enter idle states. At any point in time, the operator of the first mobile station can simply press a button on the first mobile station and say, “Hey what are you up to?” and the operator of the second mobile station can hear the voice message immediately and respond. However, a Push-to-Talk application cannot properly operate with a slotted mode that has a minimum period of 1.28 seconds.
In order to perform fast messaging in gaming applications and Push-to-Talk services, the latest generation of mobile stations are capable of entering a reduced slot cycle mode (or negative slot cycle mode) when the mobile station is in a slotted mode of operation. In reduced slot cycle mode, the mobile station selects a reduced slot cycle index, r, between −4 and 7. As before, the slot cycle index, r, gives the period, P, of the slotted mode of operation according to the equation:P=(2)r×1.28 seconds.  [Eqn. 2]Because the slot cycle index, r, can be a negative value, slot cycle periods of less than 1.28 seconds are possible. For example, if the reduced slot cycle index, r, is −4, the reduced slot cycle period of the slotted mode is 80 milliseconds. If the reduced slot cycle index, r, is −3, the reduced slot cycle period of the slotted mode is 160 milliseconds. If the reduced slot cycle index is −2, the reduced slot cycle period of the slotted mode is 320 milliseconds, and so forth.
Unfortunately, the widespread use of reduced slot cycle mode by a large number of mobile stations creates considerable scheduling problems in the base station. When paging slot cycles are 1.28 seconds or greater, the base station has the luxury of being able to flexibly schedule the transmission of paging messages to nearby mobile stations. However, when slot cycles are only 80 milliseconds long, the base station is less able to schedule transmissions in an optimal manner. Under some heavily loaded conditions, the benefits of shorter paging cycles become reduced.
Furthermore, certain applications, such as QCHAT, may require a first group of mobile stations to monitor the paging channel of a base station more frequently than a second group of mobile stations. Continually operating the second group of mobile stations in the reduced slotted mode unnecessarily drains the batteries of the second group of mobile stations and reduces battery life. However, operating the first group of mobile stations in a normal mode of operation (non-reduced slotted mode) has a negative impact on application performance.
Therefore, there exists a need for improved systems and methods of controlling the use of reduced slot cycle mode of operation by mobile stations in a wireless network.